Method of electroplating plastic substrate

ABSTRACT

Provided is a method of electroplating a plastic substrate, wherein the treatment time of processes including coarsening, copper plating, nickel plating, etc. is decreased, and a semi-gloss nickel plating process (a semi-gloss nickel plating layer) in a conventional electroplating process is obviated. Also, production capacity is remarkably increased and the plating cost and use of chromium are decreased, thus lowering environmental pollution. Furthermore, the process time and the thickness of the copper and nickel plating layers are decreased, and the electroplated surface of the plastic substrate by PVD is eco-friendly and exhibits superior heat resistance, corrosion resistance, and anti-scratching and anti-oxidation properties. Moreover, as the temperature and the gas content are adjusted in the PVD process, the resulting PVD layer can show various vivid colors having a metallic and 3D appearance, and conventional monotonous color defects can be overcome.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of surface-treating a plasticsubstrate and, more particularly, to a method of electroplating aplastic substrate.

This application claims the benefit of Chinese Patent Application No. CN201410479814.8, filed Sep. 19, 2014, which is hereby incorporated byreference in its entirety into this application.

2. Description of the Related Art

Conventional electroplating for a plastic substrate is comparativelycomplicated and requires a large amount of energy and a long period oftime. When such a plastic substrate electroplating process is performedfor 3˜4 hr, plating on the surface of the plastic substrate iscompleted.

The color, which may be shown by the conventional plastic substrateelectroplating process, is very limited and is relatively monotonous,making it impossible to satisfy current demands for beautiful goods.

Also, the conventional plastic substrate electroplating process isproblematic because poisonous harmful chemicals, such as hexavalentchromium, trivalent chromium, and sulfuric acid, are contained,undesirably causing serious damage to the natural environment and thehuman body.

However, the use of harmful chemicals is currently inevitable in theplastic substrate electroplating process.

Among chemicals used for the conventional electroplating process,hexavalent chromium is a significantly harmful environmental pollutant,and most leading enterprises ban the use of hexavalent chromium.Furthermore, trivalent chromium is adopted to thus reduce environmentalpollution, but trivalent chromium is merely less harmful compared tohexavalent chromium and is still eco-unfriendly.

Typical examples of the chromium compound may include a hexavalentchromium compound such as chromic anhydride, potassium dichromate orsodium dichromate, a trivalent chromium compound such as chromic oxide(Cr₂O₃), and a divalent chromium compound such as chromous oxide. Themost highly toxic chromium compounds are hexavalent chromium followed bytrivalent chromium.

According to studies, chromium is an element required in a small amountby mammals. Chromium compounds should not be taken in large amounts. Inthe case where such a chromium compound comes into direct contact withthe skin of the human body, the skin suffers from excessive stimulus oreven a burn.

Furthermore, the conventional electroplating process generates a largeamount of polluted water, and consumes significant power and water. Afully automated cyclic production line enables the processing of aplating surface area over about 20,000 m² per month and discharges about2,000 tons of wastewater.

Due to the discharge of a large amount of wastewater, water resourcesare wasted, and the environment is seriously polluted.

Thus, there is a need for improvements or alternatives to theconventional electroplating process.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made keeping in mind theabove problems including low productivity relative to the process timein conventional plastic substrate electroplating methods, and an objectof the present invention is to provide a method of electroplating aplastic substrate, which may achieve metallization of the surface of aplastic substrate, may reduce the process time, may remarkably increasethe production capacity, and may decrease environmental pollution andharm to the human body, and also which is improved and adapted for thesurface conditions of platable plastics such as ABS, PP, etc.

In order to accomplish the above object, the present invention providesa method of electroplating a plastic substrate, comprising: (1)subjecting a plastic substrate to degreasing, hydrophilic etching, andsurface coarsening, thus oxidizing and releasing a butadiene componenton the surface of the plastic substrate to thereby form a spherical holein the surface of the plastic substrate so that the surface of theplastic substrate satisfies electroless nickel plating attachmentconditions; (2) subjecting the plastic substrate to neutralization toremove chromic acid from the surface thereof, and then to activationusing a palladium colloid solution, so that highly active metalpalladium colloid particles are effectively adsorbed to the surface ofthe plastic substrate to form an activated surface and to form a uniformnickel alloy by electroless nickel plating; (3) subjecting the plasticsubstrate to peptization to dissolve the outer layer component adsorbedto a palladium colloid nucleus so as to expose palladium, and then toelectroless nickel plating, so that a deposition reaction progresses,and nickel sulfate and sodium hypophosphite in the electroless nickelplating solution react in the presence of a palladium catalyst to thusform a 0.3 μm thick electroless nickel plating layer, whereby thesurface of the plastic substrate becomes conductive and thus allows forelectroplating, followed by copper pyrophosphate plating, so that theelectroless nickel plating layer is plated with a copper layer toenhance current-loading capacity; (4) subjecting the plastic substrateto copper electroplating using gloss copper to form a thin mold markthereon using high brightness and superior filling capacity of the glosscopper, and then to nickel plating using gloss nickel to form a nickelplating layer thereon, so that the lower layers are protected andcorrosion resistance of the product is improved; and (5) subjecting theplastic substrate to chromium electroplating or physical vapordeposition (PVD), wherein the surface of the plastic substrate undergoesPVD or undergoes chromium electroplating and then PVD.

In (2), neutralization is performed using a composition composed mainlyof 30 ml/L of hydrochloric acid for an immersion time of 45˜50 sec, thetemperature of the electroplating solution is room temperature; andpalladium colloid solution treatment is performed using a compositioncomposed mainly of 35˜50 ppm of a palladium colloid solution and 200˜300g/L of hydrochloric acid at 20˜30° C. for an immersion time of 2˜2.5min, and is carried out in cyclic operation using a cotton filter orfiber filter pump. When not in use for a long period of time, the pumpfor cyclic operation is stopped, 5˜10 L of hydrochloric acid is added,and the amount of tin chloride is controlled to the upper limit, afterwhich the plating bath is covered with a lid.

In (3), peptization is performed using a composition composed mainly of100 g/L of sulfuric acid at 45˜52° C. for an immersion time of 1˜2 min,and is carried out in cyclic operation using a cotton filter or fibercore filter pump; and electroless nickel plating is performed using acomposition composed mainly of 27˜31 g/L of nickel sulfate, 12˜18 g/L ofsodium hypophosphite, 30˜50 g/L of sodium citrate, and 30˜40 g/L ofammonium chloride at 36˜40° C. for an immersion time of 4˜5 min, and iscarried out in cyclic operation using a cotton filter or fiber filterpump. Also, in the electroless nickel plating solution, nickel ions andhypophosphite ions react directly, sodium citrate is a complexing agentof the nickel ions, and aqueous ammonia of ammonium chloride functionsas a pH buffer system. Further, the concentration of the dissociatednickel ions in the electroless nickel plating solution is relativelylow, and most of the nickel ions are complexed with the citrate ions andare thus present in a complex phase, and only the dissociated nickelions may undergo a redox reaction with the hypophosphite ions in thepresence of a catalyst. As the chemical reaction proceeds, the nickelions are consumed, and the complexed nickel ions are dissociated again,so that the nickel ions are maintained at a predetermined concentration,thereby ensuring a stable reaction rate of electroless nickel. Also,copper pyrophosphate plating is performed using a copper pyrophosphateplating solution comprising 30˜36 g/L of copper pyrophosphate and200˜240 g/L of potassium pyrophosphate under conditions of a temperatureof 45˜55° C., a cathode current density of 0.5˜1.0 A/dm², and anelectroplating time of 2˜4 min, and a cotton filter is washed every weekand is replaced upon washing the plating bath.

In (4), gloss copper treatment is performed using a composition composedmainly of 160˜240 g/L of copper sulfate CuSO₄.5H₂O, 40˜90 g/L ofsulfuric acid H₂SO₄, 30˜120 ppm of a chloride ion Cl⁻, 3˜10 ml/L of abrightener A.A-MU, 0.3˜0.6 ml/L of a brightener A.A-A, and 0.3˜0.6 ml/Lof a brightener A.A-B, under conditions of a plating solutiontemperature of 18˜35° C., a cathode current density of 1˜8 A/dm², and anelectroplating time of 7.5˜8.5 min; and gloss nickel treatment isperformed using a composition composed mainly of 270˜290 g/L of nickelsulfate NiSO₄.6H₂O, 45˜55 g/L of nickel chloride NiCl₂.6H₂O, 37˜45 g/Lof boric acid H₃BO₃, 0.3˜0.5 ml/L of a brightener TD-100, 8˜10 ml/L of asoftener TD-100, and 0.5˜2.0 ml/L of a wetter TD-100, under conditionsof a plating solution temperature of 50˜65° C., a cathode currentdensity of 2˜8 A/dm², and an electroplating time of 5˜6 min. Duringelectroplating the plastic substrate, the copper plating and the nickelplating are performed, after which two water washings and individual ionexchange resin processes are carried out, thus recovering the copperions and the nickel ions in the production line so as to be recycled andcirculating water used for the water washing.

Also, (5) is performed in two types, one type of which is implemented insuch a manner that the nickel plating is completed, and chromium platingis performed and then PVD is conducted on the chromium plating layer,and the other type of which is implemented in such a manner that thenickel plating is completed, and PVD is directly performed withoutchromium electroplating. In the former type, chromium plating isperformed using a composition composed mainly of 140˜160 g/L of aTRI-COM M primary salt, 70˜100 ml/L of a TRI-COM CA complexing agent,225˜275 g/L of a TRI-COM T conductive salt, and 0.5˜2.0 ml/L of aTRI-COM WA wetter, under conditions of a process temperature of 30˜38°C., a cathode current density of 8˜15 A/dm², and an electroplating timeof 2˜6 min.

According to the present invention, the treatment time of processesincluding coarsening, copper plating, nickel plating, etc. can bedecreased, and a semi-gloss nickel plating process (a semi-gloss nickelplating layer) in a conventional electroplating process can be obviated.

Also, the plating process can be completed by operating the fullyautomated production system for 45˜55 sec in the present inventioncompared to 60˜80 sec in the conventional plastic electroplatingprocess, thereby remarkably increasing the production capacity anddecreasing the plating cost. Furthermore, the use of chromium islowered, thus reducing environmental pollution.

Moreover, compared to conventional electroplating methods, the processtime and the thickness of the copper and nickel plating layers aredecreased. Although hardness and corrosion resistance of a conventionalplating layer do not satisfy the process standards, the defects of theconventional plating process are solved by adopting a PVD processthrough various experiments. The electroplated surface of the plasticsubstrate using PVD is eco-friendly and exhibits superior heatresistance, corrosion resistance, and anti-scratching and anti-oxidationproperties. Moreover, as the temperature and the gas content areadjusted in the PVD process, the resulting PVD layer can show variousvivid colors having a metallic and three-dimensional (3D) appearance,and monotonous color defects in the conventional plastic electroplatingprocess can be overcome.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a flowchart illustrating a process of electroplating a plasticsubstrate according to the present invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS

As illustrated in FIG. 1, a method of electroplating a plastic substrateaccording to an embodiment of the present invention is specified below.

1) Degreasing a plastic substrate is performed to remove pollutants suchas fingerprints and impurities from the surface of the plastic substrateand to carry out a swelling action on the plastic substrate.

2) Subjecting the plastic substrate to hydrophilic treatment isperformed after 1). Specifically, the plastic substrate is etched.

3) Coarsening the plastic substrate is performed after 2). Specifically,the butadiene component of the surface of the plastic substrate isoxidized to thus be released, thereby forming spherical small holes inthe surface of the plastic substrate, so that the surface of the plasticsubstrate is coarsened so as to be adapted for attaching an electrolessnickel plating layer thereto. This process is regarded as important interms of having an influence on the bonding force between the platinglayer and the surface of the plastic substrate. The main composition forthe coarsening process comprises chromic acid and sulfuric acid. Theamounts thereof may significantly affect the quality of platingproducts. A coarsening solution is composed of 390˜440 g/L of chromicanhydride and 390˜420 g/L of sulfuric acid, and the temperature of theplating solution is maintained at 63˜70° C., and the immersion time isset to 3.5˜4.5 min. The amount of trivalent chromium is controlled to10˜20 g/L, and a coarsening bath must be equipped with a trivalentchromium remover. The typical service life of the coarsening solution isthree months. Since the butylene component of the plastic substrate isdissolved in a large amount, the color of the product turns to deepbrown and the viscosity and specific gravity thereof are increased.Hence, half of the bath solution has to be replaced at an interval of3˜5 months.

4) Neutralizing the plastic substrate is performed after 3).Specifically, as chromic acid is removed from the surface of the plasticsubstrate, chromic acid pollution that affects some subsequent processesmay be decreased. The main composition for neutralization comprises 30ml/L of hydrochloric acid. The immersion time is 45˜50 sec, and thetemperature of the plating solution is room temperature.

5) Activating the plastic substrate (with a palladium colloid solution)is performed after 4). Specifically, highly active metal palladiumcolloid particles are easily adsorbed to the surface of the plasticsubstrate treated in 4), thus forming an activated surface and enablingthe production of a relatively uniform nickel plating layer in anelectroless nickel plating process. The main composition for thepalladium colloid solution treatment comprises 35˜50 ppm of a palladiumcolloid solution and 200˜300 g/L of hydrochloric acid. This process isperformed at 20˜30° C. for an immersion time of 2˜2.5 min, and may becarried out in cyclic operation using a cotton filter or fiber filterpump. The cotton filter is washed at an interval of three days, and isreplaced with a new cotton filter every month. When not in use for along period of time, the pump for cyclic operation is stopped. Uponstopping the system, 5˜10 L of hydrochloric acid is added depending onthe volume of the bath, and the amount of tin chloride is controlled tothe upper limit, after which the plating bath is covered with a lid.

6) Subjecting the plastic substrate to peptization is performed after5). Specifically, the outer layer component adsorbed to a palladiumcolloid nucleus is dissolved to expose palladium, and electroless nickelplating is promoted, and thus a deposition reaction progresses. The maincomposition for the peptization process comprises 100 g/L of sulfuricacid. This process is conducted at 45˜52° C. for an immersion time of1˜2 min, and is carried out in cyclic operation using a cotton filter orfiber filter pump, and the flow rate of the pump is set to at least 4times/hr. The cotton filter is washed once a week, and is replaced witha new cotton filter every month, and the plating solution is completelyreplaced at an interval of 15˜20 days.

7) Subjecting the plastic substrate to electroless nickel plating isperformed after 6). Specifically, nickel sulfate and sodiumhypophosphite in the electroless nickel plating solution react in thepresence of a palladium catalyst, thus forming an electroless nickelplating layer. As the surface of the plastic substrate may becomeconductive, it is possible to perform a typical electroplating processthereon. The main composition for the electroless nickel plating processcomprises 27˜31 g/L of nickel sulfate, 12˜18 g/L of sodiumhypophosphite, 30˜50 g/L of sodium citrate, and 30˜40 g/L of ammoniumchloride. This process is conducted at 36˜40° C. for an immersion timeof 4˜5 min, and is carried out in cyclic operation using a cotton filteror fiber filter pump. The cotton filter is washed once a day, and isreplaced with a new cotton filter every week. The direct reactioncomponents in the electroless nickel plating solution are nickel ionsand hypophosphite ions, and sodium citrate is a complexing agent of thenickel ions, and aqueous ammonia of ammonium chloride functions as a pHbuffer system. The concentration of the dissociated nickel ions in theelectroless nickel plating solution is relatively low, and most of thenickel ions are complexed with the citrate ions and are thus present ina complex phase, and only the dissociated nickel ions may undergo aredox reaction with the hypophosphite ions in the presence of acatalyst. As the chemical reaction proceeds, the nickel ions areconsumed, and the complexed nickel ions are dissociated again, so thatthe nickel ions are maintained at a predetermined concentration, therebyensuring a stable reaction rate of electroless nickel. If the ratio ofindividual components is unbalanced, electroless nickel may bedecomposed, and also a chemical reaction may occur while forming thecatalytic reaction center due to the bath solution and the otherimpurities contained in the bath, in addition to the chemical reactionof the surface of the part to be plated. Hence, the rotational rate ofthe pump for cyclic operation is maintained, and the amounts of thecomponents, operating conditions, and periodic bath washing are strictlycontrolled, thereby maintaining the preferable reaction rate. When theamount of sodium hypophosphite that is a chemical reaction byproduct ishigh, the chemical reaction is suppressed and thus plating omission maytake place. Accordingly, the solution is cleanly maintained, and sidereactions and self-reaction are decreased as much as possible, so thatthe amount of sodium hypophosphite is not increased, thus prolonging theservice life of the solution. To this end, the bath has to be cautiouslyhandled upon washing, and the inside of the bath is neither damaged norroughly handled. Furthermore, the portion (especially the edge or theangled portion) of the bath and the filter pump are checked in terms ofwhether there is deposited nickel. If there is deposited nickel, it mustbe removed.

8) Subjecting the plastic substrate to copper pyrophosphate plating isperformed after 7). Specifically, the electroless nickel plating layerobtained in 7) is as thin as 0.3 μm, and may be further plated with acopper layer to enhance current-loading capacity so that the subsequentprocesses are made easy. A copper pyrophosphate plating solution for thecopper pyrophosphate plating process is composed mainly of 30˜36 g/L ofcopper pyrophosphate and 200˜240 g/L of potassium pyrophosphate. Thiselectroplating process is performed at 45˜55° C. for 2˜4 min under acathode current density of 0.5˜1.0 A/dm². The cotton filter is washedevery week, and is replaced when the plating bath is washed.

9) Subjecting the plastic substrate to copper plating (with glosscopper) is performed after 8). Specifically, gloss copper enables theformation of a thin mold mark on the surface of the plastic substrateusing high brightness and superior filling capacity thereof, and maydecrease inner stress of the plating layer. The main composition for thegloss copper plating process includes a gloss copper mixture availablefrom DEYUANBAO Chemical, comprising 160˜240 g/L of copper sulfateCuSO₄.5H₂O, 40˜90 g/L of sulfuric acid H₂SO₄, 30˜120 ppm of a chlorideion Cl⁻, 3˜10 ml/L of a brightener A.A-MU, 0.3˜0.6 ml/L of a brightenerA.A-A, and 0.3˜0.6 ml/L of a brightener A.A-B. The temperature of theplating solution is 18˜35° C., the cathode current density is 1˜8 A/dm²,and the electroplating time is 7.5˜8.5 min.

10) Subjecting the plastic substrate to nickel plating (with glossnickel) is performed after 9). Specifically, nickel plating is conductedon the surface of the plastic substrate so that the lower layers areprotected and corrosion resistance of the product may be improved. Themain composition for the gloss nickel plating process includes a nickelmixture available from TUODONG Science and Technology, comprising270˜290 g/L of nickel sulfate NiSO₄.6H₂O, 45˜55 g/L of nickel chlorideNiCl₂.6H₂O, 37˜45 g/L of boric acid H₃BO₃, 0.3˜0.5 ml/L of a brightenerTD-100, 8˜10 ml/L of a softener TD-100, and 0.5˜2.0 ml/L of a wetterTD-100. The temperature of the plating solution is 50˜65° C., and thecathode current density is 2˜8 A/dm², and the electroplating time is 5˜6min. In the process of electroplating the plastic substrate according tothe present invention, copper plating and nickel plating are performed,followed by two water washings and individual ion exchange resinprocesses, thus recovering the copper ions and the nickel ions in theproduction line so as to be recycled and circulating water used for thewater washing.

11) Subjecting the plastic substrate to chromium plating or PVD isperformed after 10). Specifically, in the present process, the surfaceof the substrate treated in 10) may be subjected to PVD so as to obtainhigher hardness, corrosion resistance, and anti-oxidation properties.Alternatively, the surface of the substrate treated in 10) may besubjected to chromium plating (to prevent oxidation of the nickel layerand to enhance hardness and corrosion resistance), and then to PVD. Morespecifically, one of the two types as above is performed in such amanner that the previous process 10 (the nickel plating process) iscompleted, after which chromium plating is implemented and then PVD isperformed on the chromium plating layer. The other type is performed insuch a manner that the previous process 10 (the nickel plating process)is completed, after which PVD is implemented directly without chromiumplating.

In particular, the main composition for the chromium plating processincludes a plating mixture available from MENGXIANG, comprising 140˜160g/L of a TRI-COM M primary salt, 70˜100 ml/L of a TRI-COM CA complexingagent, 225˜275 g/L of a TRI-COM T conductive salt, and 0.5˜2.0 ml/L of aTRI-COM WA wetter. The process temperature is 30˜38° C., the cathodecurrent density is 8˜15 A/dm², and the electroplating time is 2˜6 min.The trivalent chromium plating process is performed instead ofhexavalent chromium plating techniques that cause serious pollution,thus exhibiting high environmental protection performance, and yieldinga plating layer with a bright color and high gloss. The resultingproduct may operate at very low metal concentration, thereby loweringthe chromium metal wastewater processing costs.

The material used in the final PVD process may be selected from amongeco-friendly metal materials, such as a zirconium metal material, atitanium metal material, a chromium metal material, and a tin metalmaterial, depending on the market demand. The PVD process enables apredetermined color to be imparted to the PVD layer to thus satisfy themarket demand, by adjusting the amounts of argon and nitrogen in a PVDchamber, and the process temperature and time. The reason why the PVDprocess is adopted is that the metal used therefor, such as titanium orzirconium, is eco-friendly and is thus harmless to the human body andmanifests comparatively high corrosion resistance, anti-oxidationproperties, heat resistance, and anti-scratching properties (PVD may beselected from among medium frequency ion deposition, multi-arc magnetrondeposition, and magnetron medium frequency deposition). In the presentprocess, the nickel plating layer or the chromium plating layer may besubjected to a kind of PVD for stripe processing, thus improving theouter appearance of the product.

Even when new methods are created by combining any one step of theembodiments with the technical solution of the invention on the basis ofthe above embodiments by the technicians in the art, they areincorporated in the scope of the present invention by the presentapplicant. In order to simplify the description of the presentapplication, other exemplary methods of these steps are not listed.

The method of electroplating the plastic substrate according to thepresent invention is advantageous as follows. First, the treatment timeof processes including coarsening, copper plating, nickel plating, etc.is decreased, and a semi-gloss nickel plating process (a semi-glossnickel plating layer) in the conventional electroplating process isobviated.

Second, the plating process may be completed by operating the fullyautomated production system for 45˜55 sec in the present inventioncompared to 60˜80 sec in the conventional plastic electroplatingprocess, thereby remarkably increasing the production capacity andreducing the plating cost. Furthermore, the use of chromium isdecreased, thus lowering the environmental pollution. Third, compared toconventional electroplating methods, the process time and the thicknessof the copper and nickel plating layers are decreased. Although hardnessand corrosion resistance of a conventional plating layer do not satisfythe process standards, the defects of the conventional plating processare solved by adopting the PVD process through various experiments.Moreover, the electroplated surface of the plastic substrate by PVD iseco-friendly and exhibits superior heat resistance, corrosionresistance, and anti-scratching and anti-oxidation properties.Furthermore, as the temperature and the gas content are adjusted in thePVD process, the resulting PVD layer may show various vivid colorshaving a metallic and 3D appearance, and monotonous color defects in theconventional plastic electroplating process may be overcome.

The technical solution and the technical effects according to thepresent embodiments are different from the conventional techniques interms of the following: metallization of the surface of the plasticsubstrate may be achieved, thus reducing the process time necessary forthe conventional process, drastically increasing the productioncapacity, and decreasing the environmental pollution and harm to thehuman body. Hence, the present process is adapted for the surfaceconditions of platable plastics, such as ABS, PP, etc.

Although the preferred embodiments of the present invention regardingthe method and the system structure have been disclosed for illustrativepurposes, those skilled in the art will appreciate that variousmodifications, additions and substitutions are possible, withoutdeparting from the scope and spirit of the invention as disclosed in theaccompanying claims.

The present invention is not limited to the above method, and allembodiments that implement the object of the present invention using thestructure and the method similar to the present invention areincorporated in the scope of the present invention.

What is claimed is:
 1. A method of electroplating a plastic substrate,comprising: (1) subjecting a plastic substrate to degreasing,hydrophilic etching, and coarsening, wherein a surface of the plasticsubstrate is degreased, etched and coarsened, and thus a butadienecomponent on the surface of the plastic substrate is oxidized andreleased, thereby forming a spherical hole in the surface of the plasticsubstrate, so that the surface of the plastic substrate satisfieselectroless nickel plating attachment conditions; (2) subjecting theplastic substrate to neutralization and activation, wherein thecoarsened plastic substrate is neutralized to remove chromic acid fromthe surface thereof, and then activated using a palladium colloidsolution, so that highly active metal palladium colloid particles areadsorbed to the surface of the plastic substrate to form an activatedsurface and to form a uniform nickel plating layer by electroless nickelplating; (3) subjecting the plastic substrate to peptization,electroless nickel plating, and copper pyrophosphate plating, whereinthe plastic substrate having the nickel plating layer is subjected topeptization to dissolve the outer nickel plating layer adsorbed to apalladium colloid nucleus so as to expose palladium, after which adeposition reaction proceeds and then nickel sulfate and sodiumhypophosphite in an electroless nickel plating solution react in thepresence of a palladium catalyst to form a 0.3 μm thick electrolessnickel plating layer, so that the surface of the plastic substratebecomes conductive and thus allows for electroplating, after which theelectroless nickel plating layer is plated with a copper layer using acopper pyrophosphate plating solution to enhance current-loadingcapacity; (4) subjecting the plastic substrate to copper electroplatingand nickel plating, wherein the plastic substrate is electroplated withcopper, and then plated with nickel to form a nickel plating layer onthe surface thereof, so that lower layers are protected and corrosionresistance of a product is improved; and (5) subjecting the plasticsubstrate to chromium electroplating or physical vapor deposition (PVD),wherein the surface of the plastic substrate is subjected to PVD or tochromium electroplating and then PVD.
 2. The method of claim 1, whereinin (2), the neutralization is performed using a composition comprising30 ml/L of hydrochloric acid for an immersion time of 45˜50 sec, and theactivation is performed using a composition comprising 35˜50 ppm of apalladium colloid solution and 200˜300 g/L of hydrochloric acid at20˜30° C. for an immersion time of 2˜2.5 min, and is carried out incyclic operation using a cotton filter or fiber filter pump, and whennot in use for a long period of time, the pump for cyclic operation isstopped, 5˜10 L of hydrochloric acid is added, and a plating bath iscovered with a lid.
 3. The method of claim 1, wherein in (3), thepeptization is performed using a composition comprising 100 g/L ofsulfuric acid at 45˜52° C. for an immersion time of 1˜2 min, and iscarried out in cyclic operation using a cotton filter or fiber corefilter pump, the electroless nickel plating is performed using acomposition comprising 27˜31 g/L of nickel sulfate, 12˜18 g/L of sodiumhypophosphite, 30˜50 g/L of sodium citrate, and 30˜40 g/L of ammoniumchloride at 36˜40° C. for an immersion time of 4˜5 min, and is carriedout in cyclic operation using a cotton filter or fiber filter pump, andin the electroless nickel plating solution, a nickel ion and ahypophosphite ion directly react, sodium citrate is a complexing agentof the nickel ion, aqueous ammonia of ammonium chloride functions as apH buffer system, the dissociated nickel ion undergoes a redox reactionwith the hypophosphite ion in the presence of a catalyst, the nickel ionis consumed by a chemical reaction and the complexed nickel ion isdissociated again, so that the nickel ion is maintained at apredetermined concentration, thus ensuring a stable reaction rate ofelectroless nickel, and the copper pyrophosphate plating is performedusing the copper pyrophosphate plating solution comprising 30˜36 g/L ofcopper pyrophosphate and 200˜240 g/L of potassium pyrophosphate underconditions of a temperature of 45˜55° C., a cathode current density of0.5˜1.0 A/dm², and an electroplating time of 2˜4 min, and a cottonfilter is washed every week and is replaced upon washing a plating bath.4. The method of claim 1, wherein in (4), the copper electroplating isperformed using a composition comprising 160˜240 g/L of copper sulfateCuSO₄.5H₂O, 40˜90 g/L of sulfuric acid H₂SO₄, and 30˜120 ppm of achloride ion Cl⁻, under conditions of a plating solution temperature of18˜35° C., a cathode current density of 1˜8 A/dm², and an electroplatingtime of 7.5˜8.5 min, the nickel plating is performed using a compositioncomprising 270˜290 g/L of nickel sulfate NiSO₄.6H₂O, 45˜55 g/L of nickelchloride NiCl₂.6H₂O, 37˜45 g/L of boric acid H₃BO₃, 0.3˜0.5 ml/L of abrightener, 8˜10 ml/L of a softener, and 0.5˜2.0 ml/L of a wetter, underconditions of a plating solution temperature of 50˜65° C., a cathodecurrent density of 2˜8 A/dm², and an electroplating time of 5˜6 min, andduring electroplating the plastic substrate, the copper plating and thenickel plating are performed, after which two water washings andindividual ion exchange resin processes are carried out, thus recoveringthe copper ion and the nickel ion in a production line so as to berecycled and circulating water used for the water washing.
 5. The methodof claim 1, wherein (5) is performed in two types, one type of which isperformed in such a manner that the nickel plating is completed, afterwhich chromium electroplating is performed and then PVD is conducted ona chromium plating layer, and the other type of which is performed insuch a manner that the nickel plating is completed, after which PVD isperformed directly without chromium electroplating.